These MP Board Class 11th Chemistry Notes for Chapter 3 Classification of Elements and Periodicity in Properties help students to get a brief overview of all the concepts.
MP Board Class 11th Chemistry Notes Chapter 3 Classification of Elements and Periodicity in Properties
→ Periodic table is the arrangement of keeping similar elements together.
→ Dobereiners’s Triad : Dobereiner (1829) classified groups of three elements (triad) with similar physical and chemical properties. He also observed, that in each triad the atomic mass of the middle element was an average value of the other two elements.
→ Long form of Periodic Table : This form is based on Bohr Bury’s electronic concept. This periodic table consists of 7 periods and 18 groups. Each period starts with the filling of a new quantum number (n) and ends with the complete filling of outermost shell. In this, elements are arranged into four blocks (y-block,p-block, rf-block and^block) on the basis of electronic configuration.
→ Of all the known elements 78% of metals are placed on the left side of the periodic table.
→ Electron gain enthalpy (Electron-affinity) generally becomes more negative in a period and becomes less negative in a group.
→ Ionisation enthalpy (Ionisation energy) increases in a period, and decreases in a group.
→ Newland’s law of octaves: On arranging the elements in the increasing order of atomic mass the eighth and the first element shows periodicity like the eighth note of music.
→ Lother Meyer Curve : Atomic volume of elements are a periodic function of their atomic number.
→ Mendeleev’s Periodic Table : Mendeleev in 1869 stated that the physical and chemical properties of elements are a periodic fuhction of their atomic mass.
→ Period : Seven horizontal rows in which elements are arragned in the increasing order of atomic mass.
→ Group: Nine vertical columns in which 1 to 7 has subgroups A and B and 8lh group has three elements. Later Zero group was added.
→ Modern periodic-law : Physical and chemical properties of elements are periodic functions of their atomic numbers. Moseley proposed it in 1913.
→ Modern periodic table: Elements are placed according to their electronic structure. In long form 7 periods and 18 vertical columns (groups) are present.
→ Classification of elements :
- s-block elements : Elements having last electron in s sub¬shell. Configuration of last shell is ns1 or 2.
- p-block elements : Electrons are filled in p-subshell of outermost orbit. Configuration is ns2 np1 to 6.
Elements of 5-block and p-block are commonly known as typical elements.
- Transition elements : Situated in between s- and p-block. There are 10 vertical rows in rf-block. Two outer shells are incomplete. General configuration (outer shell) is (n -1) 1 to 10.
- Inner transition elements : Also known as f-block elements. Three outer shells are incomplete. Last electrons are filled in (n -2) f subshells.
→ Ionization potential: Required energy to pull most loosely bounded electron out in isolated gaseous atom is called I.P. In period from left to right, its value increases while in group on moving below its value decreases.
→ Electron affinity: Energy released in accepting one electron by gaseous atom is called electron
affinity. Its value decreases in groups on moving below while in periods on moving left to right increases. .
→ Electronegativity: Tendency to accept electron is called electronegativity. Its value increases in periods from left to right and in groups decreases in below.
→ Atomic radii : Half of the length of single covalent bond exist between two atoms in a molecule. Atomic radii increases in groups on moving below while in periods from left to right, it decreases.